1. Field of the Invention
The present invention relates to a temperature sensor, and more particularly, it relates to a temperature sensor which utilizes the temperature coefficient of resistance provided by a resistor.
2. Description of the Background Art
A temperature sensor of background interest to the present invention is formed by a ceramic insulating substrate, which is provided thereon with a resistive pattern. Since the resistive pattern is made of a material which has an appropriate temperature coefficient of resistance, it is possible to sense a temperature change in terms of a change of the resistance value of the resistive pattern.
In general, the material for the resistive pattern of such a temperature sensor is mainly prepared from a noble metal such as platinum. For example, paste containing such a noble metal is used to form a resistive pattern on an insulating substrate by printing, and the resistive pattern is thereafter fired.
However, noble metals such as platinum are disadvantageously high-priced.
To avoid the high cost of noble metals, the inventors have tried to prepare the material for such a resistive pattern from a low-priced base metal.
A typical low-priced base metal, copper, for example, has only a small resistivity value of .rho.=1.72 .mu..OMEGA.cm at 20.degree. C. although its temperature coefficient of resistance is at a relatively high level of 4330 ppm/.degree.C., and copper requires firing in a controlled atmosphere such as a nitrogen atmosphere, for example, since copper is easily oxidized in the air. Thus, copper has generally been employed only in a coil-type device, in an extremely limited field.
This also applies to nickel.